The present invention relates to cementitious binders containing calcium sulfoaluminate and at least one pozzolanic material.
Examples of such pozzolanic material include ground granulated blast furnace slag, fly ash, and silica fume, or natural pozzolans such as calcined shale, calcined clay or metakaolin.
Pozzolanic materials may be categorized as supplementary cementitious materials or as materials having latent hydraulic properties. Fly ash, ground granulated blast-furnace slag, silica fume, and natural pozzolans, such as calcined shale, calcined clay or metakaolin, are materials that, when used in conjunction with a Portland or blended cement, contribute to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both. A pozzolan is a siliceous or alumino-siliceous material, which, in finely divided form and in the presence of moisture, chemically reacts with calcium hydroxide released by the hydration of Portland cement to form calcium silicate hydrate and other cementitious compounds. Because of the slow pozzolanic reaction of some supplementary cementing materials, continuous wet curing and favorable curing temperatures may need to be provided for longer periods than normally required.
For example, it is known that ground granulated blast furnace slag (GGBFS) is considered a latently hydraulic material or binder, exhibiting hydraulic reactivity in the presence of an alkaline activator such as ordinary Portland cement (OPC) and/or a sulfate activator calcium sulfate. In the presence of calcium sulfate, the main hydration products formed are the ettringite and C—S—H phases.
It is also known that in slag cements composed of Portland cement and GGBFS, the early and medium-term mechanical performances fall as the quantity of blast-furnace slag is increased.
M. Michel et al. (“The influence of gypsum ratio on the mechanical performance of slag cement accelerated by calcium sulfoaluminate cement”, Construction and Building Materials, Vol. 25, pp 1298-1304 (2011)), disclose cementitious compositions containing GGBFS, OPC, calcium sulfoaluminate (CSA) clinker, and calcium sulfate. The compositions contain 30% OPC, 30% GGBFS, 24-34% calcium sulfoaluminate clinker, the remainder being calcium sulfate.
Korean Patent Document No. KR 10-0931008 discloses a water-permeable paving material comprising 15-25 parts by weight of an inorganic binder, 3-8 parts by weight of water, and 100 parts by weight of aggregate. The binder contains, by weight, 60-80% ultra-micro-granulated blast furnace slag, 5%-20% CSA, 0.5-5% of ethyl-vinyl acetate (EVA) based powder resin, 0.5-10% waste gypsum, and 5-20% natural lime.
Korean Patent Document No. KR 10-0896005 discloses an admixture composite for improving the strength of ready-mix concrete, the admixture containing, by weight, 55-95% fine blast-furnace slag, 2-10% calcium sulfoaluminate, and 3-35% sodium calcium sulfate (Na2Ca(SO4)2). Various sulfate sources are contemplated. Preferably, the admixture composite makes up 3-25% of the binder, by weight. The binder typically contains about 50% OPC, by weight. According to KR 10-0896005, the CSA contributes strength by creating large amounts of ettringite when used in combination with Portland cement.
These advances notwithstanding, the present inventors have recognized a need for improved, environmentally friendly, cost-effective, pozzolan-based cementitious compositions, and the subject matter of the present disclosure and claims is aimed at fulfilling this need.